1. Field of the Invention
This invention relates to systems for controlling the operation of machine tools by machine tool controllers under the control of a central data processing unit. More particularly, the present invention relates to systems for testing the machine tool controllers.
2. Description of the Prior Art
With the ever increasing automation of industry both in manufacturing and in facilities controlling and monitoring, as well as in the ever increasing automation of many aspects of life both in business offices and in homes, there is a constant demand for means for controlling the operation of a wide variety of machine tools, many at increasing operational speeds.
With the rapid advances being made in development of the large scale integrated circuit technology, resulting in bigger, more efficient, faster and less expensive integrated circuits, there has been rapidly increasing use of machine tool controllers which are microprocessors using one or a few large scale integrated circuit chips which are substantially dedicated to the machine being controlled.
The use of such machine tool controllers over the past decade has extensively replaced or at least supplemented the more traditional approach of machine tool control involving a large capacity general purpose central processor with extensive multiplexing to control a plurality of machine tools. While such multiplexing still has its place in machine tool technology, it is usually substantially slower than systems involving the plurality of dedicated machine tool controllers supervised by a central processing unit. Thus, in control systems requiring high speeds, the use of tool controllers is increasing.
One area in central processor supervised machine tool control in which additional capabilities are needed is in the testing of the machine tool controllers, and particularly in the diagnostics involved when there has been an error or failure in a machine tool controller system. The standard approach in the failure and error diagnoses involves the testing of the combination of the machine tool controller and the machine tool itself under central processor supervision. While such approaches have been found to be reasonably effective in the communications field as in the system of U.S. Pat. No. 4,042,794 for example, this approach has been less than completely desirable in machine tool controller systems. In testing the latter it is often difficult and expensive to isolate whether the failure has occurred in the machine tool itself or in the machine tool controller. This is particularly true when the machine tool controller performs complex transformation on the data provided to the controller from the central processor, e.g., the inclusion of clock pulses or other forms of encoding/decoding functions or even transformations, required for multiplexing or demultiplexing in order to make the data compatible with the machine tool itself. Likewise, in such a case, the controller would perform functions such as the separation of clock pulses or other decoding as well as demultiplexing on data received from the machine tool.
One approach towards a solution of this problem would be the extensive incorporation of sufficient hardware in the tool controller to perform diagnostics on the tool controller with a minimal intervention of the central processor. This approach has been used extensively only in cases where both read and write hardware are used in the "normal" mode. The duplicate hardware is justified by something other than diagnostic purposes (such as for full duplex communications). This follows because the need for the additional hardware substantially increases tool controller cost. U.S. Pat. No. 3,889,109 describes this type of configuration.